The present invention relates to electronic packaging for PC Cards, and more particularly to attaching PC Card covers to printed circuit boards and frames.
Typically, each PC Card consists of a printed circuit board and a frame which is enclosed by either a stamped sheet metal or a plastic material. The covering is used to protect the electronic circuitry on the printed circuit board. Referring to FIG. 1, at one end the PC Cards have a 68 pin connector 11 for attachment to a computer. Some of these cards may have another connector 12 at the opposite end to allow the computer to be coupled to an external device. Such a connector is commonly found on internal modems or facsimile cards.
As computer systems have continued to be downsized, internal spatial restrictions have required the establishment of standards for the internal accessories of the computer. The Personal Computer Memory Card International Association ("PCMCIA"), comprised of hundreds of manufacturers of memory cards and related peripheral equipment, has established PC Card standards defining the PC Card's physical outline standards, connector system and qualification test parameters, including reliability, durability and environmental test parameters. The latest PCMCIA standard, release 2.01 is incorporated here by reference. PC Cards are a key technology for adding memory, storage, and Input/Output capabilities to portable computer systems and can be used with any personal potable computer system equipped with a PCMCIA slot, including laptops, notebooks, palmtops, and tablets.
The PCMCIA has determined that the spatial standards of all PC Cards used in down-sized computers should be restricted to a rectangular space approximately 55 millimeters in width and 85 millimeters in length, which is about the size and shape of a "credit" card. The PCMCIA specifications further define the thickness of the PC Cards as one of the following types: Type 1, Type II, or Type III. The thicknesses for Type I, Type II, and Type II are 3.3, 5.0, and 10.5 millimeters respectively (see FIGS. 2A, 2B and 2C).
A Type I PC Card is typically used for various types of memory enhancements, including RAM, FLASH memory, one-time programmable memory, and electronically erasable programmable read only memory. A Type II PC Card is typically used for memory enhancements and/or for Input/Output features such as modems, LANs and host communications. A Type III PC Card is twice the thickness of the Type II and is typically used for memory enhancements and/or for Input/Output features that require a larger size, such as rotating mass storage devices and radio communication devices. Since Type I, Type II and Type II Cards all use the same interface, the size of the card chosen for the application is dependent on the miniaturization of the technology to be implemented.
In the past, the stringent qualification test parameters defined by PCMCIA in Section 3 of the Card Physical have placed limitations on the types of methods used to attach the covers of the cards to the printed circuit board and frame. The key is to provide a cover that is rugged enough to withstand the qualification and reliability testing, while being cost efficient from the manufacturing standpoint. Currently available methods of attaching the cover to the printed circuit board and frame includes both adhesive and adhesiveless solutions. The adhesive solution provides several alternative methods of attachment such as a pressure sensitive adhesive which is similar to the back of a sticky label, or a thermoplastic adhesive, both of these methods require heat and pressure to apply the adhesive. Another method of attachment is to apply a liquid adhesive such as an epoxy. However, this method incorporates a long dispense and cure cycle to set the adhesive, and furthermore requires very close process monitors.
Several adhesiveless solutions are also available today. Rather than using an adhesive, the attachment method may be designed into the cover and frame such that the cover snaps into the frame with small latches. While this solution is economical from the manufacturing standpoint, it does not satisfy the rigidity requirement set forth by the PCMCIA standards. Another adhesiveless method is to wrap the cover around the perimeter of the card such that the bottom cover and the top cover touch around the perimeter of the frame and are welded together. This solution provides a very strong assembly between the printed circuit board, frame, and cover, however, the equipment necessary for this process is very expensive due to the high tolerance required to assure the bottom and top covers touch around the entire perimeter of the card.
Therefore, it is desirable to provide an adhesiveless solution, which has a very fast manufacturing process throughput and is economical, yet complies with the PCMCIA standards for PC Cards.